Field of the Invention
present invention relates to an apparatus for producing deionized water.
Heretofore, as a method for producing deionized water, it is common to obtain deionized water by passing water to be treated through a bed packed with an ion exchange resin so that impurity ions are removed as adsorbed on the ion exchange resin. Here, it is common to employ a method of regenerating the ion exchange resin having its ion-exchanging and adsorbing abilities lowered, by means of an acid or alkali. However, this method has problems that a troublesome operation is required and that a waste liquid of the acid or alkali used for the regeneration, is discharged. Therefore, a method for producing deionized water which requires no such regeneration, is desired.
From such a viewpoint, a self-regenerating type electrodialysis deionizing method using a combination of an ion exchange resin and an ion exchange membrane has been recently noted. This method employs an electrodialyzer having anion exchange membranes and cation exchange membranes alternately arranged to form demineralizing compartments and having an ion exchanger accommodated in the demineralizing compartments, and is designed to apply a voltage while supplying water to be treated to the demineralizing compartments to carry out electrodialysis to produce deionized water, while regenerating the ion exchanger accommodated in the demineralizing compartments.
With regard to this method, there have been proposed a method of limiting a width and a thickness of a demineralizing compartment (JP-A-61-107906), a method of using ion exchange resin particles having a uniform particle size to be packed in a demineralizing compartment (JP-A-3-207487), a method of using an anion exchange resin as an ion exchange resin to be packed in a part where water to be treated is initially passed (JP-A-4-71624), a method of using a mixture of an ion exchange resin and an ion exchange fiber as an ion exchanger to be packed in a demineralizing compartment (JP-A-5-277344), and the like.
However, a purity of deionized water was not stable due to such problems that ion exchangers having the same ionic charges were aggregated each other, that ion exchange resin particles or fibers were damaged by a water stream and that efficient demineralization and regeneration could not be conducted.
In order to solve the above mentioned problems, there have been proposed a method of introducing ion exchange groups into a non-woven cloth such as polyethylene or polypropylene by graft-formation by radiation (JP-A-5-64726, JP-A-5-131120), a method of forming a sheet-like material after making a composite fibrous form of a spot-like structure of an ion exchange polymer and a reinforcing polymer (JP-A-6-79268), and the like.
According to these methods, an ion exchanger is fixed, but these methods have various defects that it is necessary to use radiation, that a step of making composite fibers is complicated, and that a mechanical strength is not always satisfactory.
Thus, an object of the present invention is to stably produce deionized water having a high purity at a low voltage by a self-regenerating type electrodialysis deionization method using a combination of an ion exchange membrane and an ion exchanger fixed without a complicated step of using radiation.